Elastic lens holder

ABSTRACT

Elastic lens holder with a lens mount and a lens, an annular groove being constructed on the circumferential surface of the lens, and there being present at the lens mount elastic segments whose free ends engage radially under pretension in the annular groove.

BACKGROUND OF THE INVENTION

a) Field of the Invention

The invention relates to a lens holder comprising a lens and a lensmount in which the lens is elastically mounted in the radial fashionover the circumferential surface of the lens.

b) Description of the Related Art

Such an embodiment is known in the widest sense from German patentapplication DE 35 21 640.

Mounting the optical elements with low stresses is a central problem inthe development of UV high-performance lenses. Mounting with lowstresses is taken to mean that as far as possible the optical elementexperiences no deformation through the mount itself, and that dynamicand thermal loads do not lead to any strains or to maladjustment of theoptical element.

A multiplicity of arrangements are known from the prior art for thepurpose of solving this problem, and in these cases an optical elementsuch as a lens is held in a mount with the aid of elastic means.

For example, German patent application DE 28 46 241 A1 discloses anarrangement in which a lens guided radially in its mount is pressedaxially against a fixed bearing surface by at least two plateletsengaging over the end region of the lens. The platelets are made from anelastic material and are held in a self-closed fashion in the mount insuch a way that they bear under pretensioning against the lens.

A thermal expansion of the lens in the axial direction can becompensated by the axially elastic bearing of the lens. Likewise,dynamic loads can be damped. In order also to permit radial thermalexpansion of the lens without the occurrence of radial stresses in thelens, which can lead to dramatic worsening of the optical imaging, theremust be adequate play in the fitting of the mount and of the lens as afunction of the different coefficients of thermal expansion. However,within this play of the fitting maladjustments can occur under theaction of radial dynamic loads.

German utility model G 86 25 896 describes a second axially elasticholder for optical components in a mount. Here, the elastic holdingelement is in the form of a closed ring which bears against the mount inthe edge region of the lens, on the one hand, and in a groove providedfor the purpose, on the other hand.

A disadvantage of this solution is that dynamic loads are transmittedvirtually undamped onto the lens via the ring, which is rigid in theradial direction.

As in the solution previously mentioned, the spring forces act to holdthe lens on the optically effective face. Since the absolute value ofthe spring force changes as a function of the thermal expansion of thelens, changed states of stress occur in the lens which fail to meet thehigh requirements placed on the imaging quality, in particular in thecase of high-performance lenses. DE 196 32 267 A1 discloses a lensholder in the case of which locating noses constructed on the lens mountbear in an engaging groove constructed on the lens (including a cementedlens cluster), in order to hold the lens in the mount in a self-closedfashion. In the case of a cemented lens cluster, the engaging groove isformed by the phase surfaces meeting at the cemented surface. In thecase of an individual lens, the engaging groove is not an actual groovebut a phase surface of the lens. The position of the lens inside themount is determined in the radial direction by a play in the fittingbetween an inner circumferential surface of the lens mount and an outercircumferential surface of the lens, and in the axial direction bypressing the edge region of an end face of the lens against a holdingprojection of the mount.

The mount is neither thermally nor mechanically stable. In the case ofexpansion and shrinkage of the lens material as a consequence of athermal load, there is necessarily a relative displacement with respectto the mount, and therefore friction, on the one hand, on the bearingsurface of the locating noses in the engaging groove of the lens and, onthe other hand, on the bearing surface of the holding projection on theend face of the lens. The backsliding caused by the friction has theeffect that the displacement takes place in an undefined fashion and thelens does not return to its initial position. For high-performancelenses, such a maladjustment is already capable of substantiallyreducing the imaging quality. The additional securing of position bymeans of adhesive renders the lens holder unsuitable for UV radiation.

Mechanical loads such as shocks are transmitted onto the lens withoutbeing damped in the radial direction. Another disadvantage is thatpressures act on the lens via its optically active end face, and thiscan lead to deformation of the lens.

German patent application DE 35 21 640 A1 discloses a holder which iselastic in the radial direction. It comprises at least three ribs whichare preferably provided distributed uniformly on the cylindricalcircumferential surface of the lens and are made from a highly elasticmaterial, advantageously from silicone rubber. These are compressed whenthe lens is installed in the mount. The mount and the lens can expanddifferently without impedance in the axial direction owing to the onlyslight indirect contact surface between the mount and the lens on thecircumferential surface of the lens.

The centering of the lens in its mount is always ensured independentlyof thermal and dynamic loads. It is also advantageous that the forcesacting act on the circumference and not on an optically effective face.In order to improve the positional stability, it is proposed to make useof a retaining ring, likewise provided with elastic ribs, or a plug-inring, which is to be bonded in, which fixes the lens additionally in theaxial direction. This becomes indispensable for lenses of relativelylarge mass, and signifies additional outlay on mounting.

However, it is not possible to make use for high-performance lenses,which require UV resistance because of the radiation used, of anyorganic materials such as, for example, adhesives, potting compounds,silicone rings and similar materials, since these decompose in the longterm under the action of UV radiation and constitute a contaminationrisk. It follows that indirect elastic mounting using organic materials,such as is known from DE 35 21 640, is not suitable for high-performancelenses.

OBJECT AND SUMMARY OF THE INVENTION

It is the primary object of the invention to create a lens holder whichis suitable, in particular, for UV lenses and in the case of which thelens is held elastically in a radial fashion at its circumferentialsurface. Moreover, the lens holder is to have a shape such that the lenscan be mounted easily and quickly and can also be effectively rinsed inthe mounted state.

The invention achieves this object for a lens holder by virtue of thefact that an annular groove is constructed on the circumferentialsurface of the lens and the elastic elements are segments which areformed on the lens mount and whose free ends engage radially in theannular groove, and the lens is held radially and axially exclusivelyvia this connection.

The formation of radially elastic segments on the lens mount itselfcreates a lens mount in which a lens can be mounted with low stresses,directly and without additional means on its circumferential surface.

The geometry of the segments is variable and can therefore be adapted incoordination with the material constants of the mount, the dimensioningof the segments and the desired spring stiffness to the existing spaceconditions for the lens mount.

The segments are of the same dimensions and engage in a radiallyuniformly distributed fashion in the annular groove introduced on thecircumferential surface, with the result that the lens itself iscentered in the lens mount. The spring stiffness of the individualsegments, and the pretensioning force exerted by them on the lens arethe same. The annular groove lies in a radial plane.

The different thermal expansions of the lens mount and the lens arecompensated in the radial direction via the spring action of thesegments, while there is no need for compensation in the axialdirection, because the contact is only linear.

By virtue of the fact that the lens is connected to the mountexclusively via the elastic segments, dynamic loads are transmitted tothe lens only with damping.

It is advantageous according to the invention when the annular groove isintroduced in the radial plane of the lens in which a radial action offorce effects the slightest bending of the optically effective faces ofthe lens. This plane is determined by means of the so-called finiteelement method.

The cross section of the groove is advantageously V-shaped with oneradius formed in the apex. It is advantageous when a larger radius isformed at the free ends of the segments with the result that the freeends come to bear in the V-groove against the edges thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Five exemplary embodiments which utilize the invention are explained inmore detail below with the aid of the drawing, in which:

FIGS. 1A to 1C show a first embodiment;

FIGS. 2A and 2B show a second embodiment;

FIGS. 3A and 3B show a third embodiment;

FIG. 4 shows a fourth embodiment; and

FIG. 5 shows a fifth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A lens mount according to FIGS. 1 to 3 is viewed in the axial direction,formed at its first end as a closed ring, while at its second end theclosed ring shape is raised by a multiplicity of slots running in theaxial direction. This slotted end constitutes an annular arrangement ofidentically dimensioned segments which can be differently shapedaccording to the invention for the individual embodiments.

The first end of the lens mount can likewise be differently shaped,depending on the structural configuration of the housing into which thelens mount is, if appropriate, to be introduced. The first end isconstructed using expert knowledge in accordance with the requiredconnecting conditions and is not intended to be the subject matter ofthe invention.

Different designs of the segments lead to a different cross section ofthe lens mount in the region of the slotted end.

A first embodiment is illustrated in FIGS. 1A to 1C. The segments are ofplate-shaped form and are angular only at their free end. Areinforcement is constructed in the region of the angle. The thickness,the length and the width of the segments are selected as a function of adesired bending characteristic and of the material of the lens mount. Asmay be seen from FIG. 1, the thickness can also differ over the length.The segments illustrated here are arranged in each case parallel to theaxis of symmetry. They could equally run angularly.

A second embodiment is illustrated in FIGS. 2A and 2B Here, the lengthof the segments is reduced by a meandering formation. However, in orderto shorten the lens mount in the axial direction in such a way it isnecessary for it to have a design with a larger diameter. Here, as well,the concrete structural dimensioning can lend the segments a desiredbending moment characteristic.

The mount can also be of bipartite form in order to be more independentin the selection of material for the segments. A third embodiment isillustrated for this purpose in FIGS. 3A and 3B. Thus, the first end ofthe lens mount can consist of a material which can be machinedeffectively (for example for the purpose of precision turning), while amaterial of higher elasticity is used for the second end.

The slot produced by the segmentation permits the lens to be rinsed inthe mounted state.

In order to mount the lens in the lens mount, the segments aresimultaneously spread apart using an aid provided for the purpose, and ahandle is used to insert the lens. There is no need for additional meansto secure the lens position, and so the mounting is quick anduncomplicated.

A design which saves even more space is illustrated for a lens mount inFIG. 4. Present here as elastic segments are three formations in theshape of circular segments on the inner circumference of the mountingring, which lie in a plane with the annular groove. A resilient actionis achieved for these segments by slots introduced in the tangentialdirection. Constructed in the middle of the slots on the formations areattachments which are adapted in shape to the annular groove. Bycomparison with that previously described, this design has the advantagethat the space requirement for the lens holder is no longer determinedin the axial direction by the dimensioning of the elastic segments.

In the exemplary embodiment illustrated in FIG. 5, the segments areindividual plates which are in the form of circular segments and aredetachably connected to the mounting ring on an end face thereof via ascrew connection. They act like the segments described in the fourthexemplary embodiment, but have two noteworthy advantages. On the onehand, this design is easier to mount, since there is no need to spreadall the segments in order to insert the lens, but it is possible withonly two segments mounted to insert the third segment easily andsubsequently fasten it. On the other hand, the segments can be fitted ona mounting ring on both end faces thereof (not illustrated in thedrawing), in order to hold two individual lenses with one lens mount.The required spacing of the lenses relative to one another thendetermines the thickness of the mounting ring.

The mounting ring need not, of course, be a plate-shaped ring, but canalso have an inner collar against whose end faces the segments bear.Likewise, the segments can also be fitted in a circumferential groove inthe mounting ring. It is important only that they all bear against themounting ring in one radial plane so that the action of their force isensured in the same plane. The number of the segments can also beselected to be higher. Likewise, other mechanical connections are alsopossible between the segments and the mounting ring.

While the foregoing description and drawings represent the preferredembodiments of the present invention, it will be obvious to one skilledin the art that various changes and modifications may be made thereinwithout departing from the true spirit and scope of the presentinvention.

What is claimed is:
 1. An elastic lens holder comprising: a lens mountand a lens against whose circumferential surface elastic, pretensionedelements bear; an annular groove being constructed on thecircumferential surface of the lens; said lens mount being formed by amounting ring and said elastic elements; said elastic elements beingsegments which in each case have a fixed end, connected to the mountingring, and a free end which engages radially in the annular groove andholds the lens radially and axially; wherein the segments form a ringwhich is closed on the side of the fixed ends and is slotted in theaxial direction on the side of the free ends.
 2. The elastic lens holderas claimed in claim 1, wherein the annular groove lies in a radial planeof the lens in which acting forces effect the slightest bending of theoptically effective faces of the lens.
 3. The elastic lens holder asclaimed in claim 1, wherein the annular groove is V-shaped with oneradius formed in the apex, and a larger radius is formed at the freeends of the segments with the result that the free ends come to bear inthe V-groove against the edges thereof.
 4. The elastic holder as claimedin claim 1, wherein the closed annular region constitutes the mountingring.
 5. An elastic lens holder comprising: a lens mount and a lensagainst whose circumferential surface elastic, pretensioned elementsbear an annular groove being constructed on the circumferential surfaceof the lens; said lens mount being formed by a mounting ring and saidelastic elements; said elastic elements being segments which in eachcase have a fixed end, connected to the mounting ring, and a free andwhich engages radially in the annular groove and holds the lens radiallyand axially; wherein the segments are formations in the shape ofcircular segments on the inner circumference of the mounting ring whichare slotted in the tangential direction and have at the center anattachment as free rend.
 6. An elastic lens holder comprising: a lensmount and a lens against whose circumferential surface elastic,pretensioned elements bear; an annular groove being constructed on thecircumferential surface of the lens; said lens mount being formed by amounting ring and said elastic elements; said elastic elements beingsegments which in each case have a fixed end, connected to the mountingring and a free end which engages radially in the annular groove andholds the lens radially and axially; wherein the segments are arrangedat the two end faces of the mounting ring, in order to hold two lenseswith one lens mount.
 7. The elastic lens holder as claimed in claim 6,wherein the segments are arranged at the two end faces of the mountingring, in order to hold two lenses with one lens mount.